Problem: 3 crayons cost $3.24. Which equation would help determine the cost of 7 crayons?
Answer: There are several equations that could help determine the cost, each with a slightly different approach. If we let $x$ represent the cost of 7 crayons, we have the following proportion: $\dfrac{x}{7}$ We have to pay $3.24 for 3 crayons, and that can be written as a proportion: $\dfrac{\$3.24}{3}$ Since the price per crayon stays the same, these two proportions are equivalent. $\dfrac{x}{7} = \dfrac{\$3.24}{3}$